1. Field of the Invention
The present invention relates to a method of producing a Nb3Sn superconducting wire rod, and a Nb3Sn superconducting wire rod. In particular, it relates to a method for producing a high critical current Nb3Sn superconducting wire rod, which can be applied to a high magnetic field magnet, and a Nb3Sn superconducting wire rod.
2. Description of the Related Art
As a conventional Nb3Sn superconducting wire rod production method, a bronze method has been widely used. The bronze method is for wire drawing to structure a wire rod to have multiple Nb filaments arranged in a Cu—Sn alloy matrix, and subsequent heat treatment to thereby allow Sn in the Cu—Sn alloy to diffuse to react with the Nb filaments, to produce Nb3Sn in at least portions of the Nb filaments. However, because the upper limit of the Sn solid solution in the Cu—Sn alloy is on the order of 16 weight %, Nb3Sn cannot be produced more than that upper limit, and there has therefore also been a limit on enhancement of its critical current value (Ic), and the like.
Accordingly, a Nb3Sn superconducting wire rod production method has previously been known that comprises: forming a composite having stacked therein an alloy or intermetallic compound of Sn and one or two or more metals selected from the group of Ti, Zr, Hf, V, and Ta, and Nb or a Nb alloy; working this composite into a wire rod; and subsequently heating it, wherein the alloy or intermetallic compound of Sn and one or two or more metals selected from the group of Ti, Zr, Hf, V, and Ta has a Sn content ranging from 20 to 75 atom %.
The above Nb3Sn superconducting wire rod production method allows producing a superconducting wire rod having a Nb3Sn phase thicker and more excellent in high magnetic field characteristics than produced with the conventional bronze method.
Refer to JP Patent No. 3945600, for example.
In the above Nb3Sn superconducting wire rod production method, however, of the constituent materials of the Nb3Sn superconducting wire rod, the proportion of Sn required for Nb3Sn production is prescribed principally in relation to the amount of Nb, but determined regardless of the amount of Cu. That is, no constituent ratios between the constituent materials including Cu are prescribed. This may lead to excess and deficiency in the Sn amount, in which case there may be a decrease in the critical current density (Jc) of the resulting Nb3Sn superconducting wire rod, or unreacted Sn may remain in the superconducting wire rod, thereby leading to a decrease in the strength of the Nb3Sn superconducting wire rod.